1. Field of the Invention
The present invention relates to a technique for making a servo locus of a magnetic head, which is controlled for positioning thereof according to servo information recorded on a magnetic disk medium of a discrete track recording (DTR) system, trace on a track which is formed between two guard bands on the magnetic disk medium.
2. Description of the Related Art
Currently, many a magnetic disk apparatus adopts a servo sector system.
The surface of a magnetic disk medium equipped on a magnetic disk apparatus is written by position information (which is called servo information, and a zone including the information is called a servo sector) indicating positions on the medium at a constant interval on a circle, and from one servo sector to the next servo sector is allocated as a zone for a data writing (which is called a data sector). And a plurality of concentric circle tracks (of the track numbers 1 through Tn, where Tn is an integer) constituted by the aforementioned circle as one track are formed on the surface. In this configuration, a pair of one servo sector and one data sector constitutes a smallest unit (i.e., a sector), with the sector being continuously formed in each track on the surface of the magnetic disk medium. Note that the above noted servo track is fixed for position as a result of servo information being written by a dedicated servo track writer and that a writing of information to a data sector between the servo sectors can be carried out under a later described control of the relevant magnetic disk apparatus.
The magnetic disk apparatus reads position information recorded in a servo sector on the above noted magnetic disk medium from a magnetic head, controls a rotation of a drive motor (i.e., a servo motor), which positions the magnetic head in the radial direction of the magnetic disk medium, so as to reduce to zero (“0”), the difference between the position information of the readout position and that of a target position, and makes the magnetic head reach a target position. A magnetic disk medium commonly use a continuous thin film medium, and therefore a data writing to the aforementioned continuous thin film medium, which is recorded by the above noted servo information, is carried out by moving the magnetic head to a servo sector belonging to a track number designated for the data writing, scanning from the servo sector to a designated servo sector (which is a servo sector belonging to a sector number designated for a data writing) on the track by rotating the magnetic disk medium, and generating a magnetic field for a writing by the magnetic head from the rear stage of the designated servo sector to the next servo sector. Note that the servo information of each servo sector includes burst information which is correction information of each servo sector for the magnetic head to reach at the center of the next servo sector. The magnetic head reads the correction information from each servo sector and minutely adjusts an arrival position of the next servo sector, thereby suppressing a positional displacement thereat. For a data reading, meanwhile, the magnetic head reads data by scanning on the data sector along the same locus as described above and converting the magnetically written data into an electrical signal by the magnetic head itself.
On a continuous thin film medium, servo sectors are formed by the servo track writer, while data sectors are formed between adjacent servo sectors within a servo sector, which is formed by the servo track writer, along a movement locus of the magnetic head passing under the above described positioning control. And the locus becomes a track of the magnetic disk medium (which is called a servo locus, while a servo sector part within the track is called a servo track and a data sector part is called a data track in the following description).
As described above, the information of the above described servo sector is recorded on a magnetic disk medium by the servo track writer. This is a process carried out prior to the shipment of a product, thus making it different from an actually shipped apparatus, and therefore a slight variance occurs in a positioning accuracy of the magnetic head against a servo sector in the case of equipping the magnetic disk medium on the actually shipping apparatus due to an error among the apparatuses of the shipping apparatuses. Therefore, a user writes positional correction information to a user writable zone (which is called a repeatable run out (RRO) zone) furnished for a servo sector in order to absorb a variance of each apparatus, thereby making it possible to suppress an occurrence of a positional displacement at a servo sector position of the magnetic head. An example of this technique is disclosed in a Laid-Open Japanese Patent Application Publication No. 09-91903. This publication has disclosed an example which calculates a positional error average value at the time of controlling a positioning at each servo sector, writes the information to the user writable zone and corrects a displacement of the servo sector based on the written information. This method allows a correction of a displacement of a servo sector, thus enabling the magnetic head to always reach at the center position when passing the servo sector position.